The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

Abstract

The photoconductor layer is an important component of direct conversion flat panel X-ray imagers (FPXI); thus, it should be carefully selected to meet the requirements for the X-ray imaging detector, and its properties should be clearly understood to develop the most optimal detector design. Currently, amorphous selenium (a-Se) is the only photoconductor utilized in commercial direct conversion FPXIs for low-energy mammographic imaging, but it is not practically feasible for higher-energy diagnostic imaging. Amorphous lead oxide (a-PbO) photoconductor is considered as a replacement to a-Se in radiography, fluoroscopy, and tomosynthesis applications. In this work, we investigated the X-ray sensitivity of a-PbO, one of the most important parameters for X-ray photoconductors, and examined the underlying mechanisms responsible for charge generation and recombination. The X-ray sensitivity in terms of electron–hole pair creation energy, W±, was measured in a range of electric fields, X-ray energies, and exposure levels. W± decreases with the electric field and X-ray energy, saturating at 18–31 eV/ehp, depending on the energy of X-rays, but increases with the exposure rate. The peculiar dependencies of W± on these parameters lead to a conclusion that, at electric fields relevant to detector operation (~10 V/μm), the columnar recombination and the bulk recombination mechanisms interplay in the a-PbO photoconductor.

Dark Current Modeling for a Polyimide—Amorphous Lead Oxide-Based Direct Conversion X-ray Detector

“…Qualitatively, the mechanism of DC decay can be explained by deep charge carrier trapping and polarization effects that cause the instantaneous electric field at the ITO/PI interface to decrease and increase within the bulk of a-PbO. As a result, we achieve two very useful effects: on the one hand, the DC decreases, and on the other hand, the collection efficiency of X-ray generated charge is improved, and W ± decreases (since it is field-dependent [ 16 , 19 ]). This is shown in Figure 4 , where W ± decreases after the instant of bias application.…”

“…A single-pixel PI/a-PbO X-ray detector [ 5 , 16 ] has been fabricated as the prototype for an a-PbO-based direct conversion flat panel imager. In Figure 1 a, a schematic diagram of the detector prototype structure is illustrated, and in Figure 1 b, an SEM cross-sectional image is shown.…”

“…W ± is derived from the total charge collected upon continuous X-ray exposure: the lower W ± is, the higher is sensitivity. More details on this analysis can be found elsewhere [ 16 , 22 , 23 ]. In a-PbO, W ± was found to depend on the applied electric field.…”

“…Despite these encouraging results, the exact transport properties of PI interfaced with photoconductors in a detector structure are not well understood [ 15 ], and concerns remain that interfacing a foreign material such as PI with a photoconductor other than a-Se, could affect detector performance. Although it is very tempting to use the PI blocking layer in conjunction with an amorphous lead oxide (a-PbO) photoconductor [ 5 , 16 , 17 , 18 ], it is challenging to predict the level of DC that will flow through a PI/a-PbO detector at a given time and electric field. Moreover, other factors affecting DC, such as possible charge accumulation at the PI/a-PbO interface, are needed to be understood.…”

Electrochemical paraquat sensor based on lead oxide nanoparticles

“…Lead oxide has been served for electrode coating due to its superior reaction sites and intrinsic chemical properties. 22 There are many oxide forms including PbO, Pb 2 O 3 , Pb 3 O 4 , and PbO 2 which can be applied in γ-ray shielding, 23 photoconductor, 24 memristor application, 25 radiation attenuation application, 26 energy-storage application, 27 and lithium ion battery. 28 The lead oxide nanoparticles (PbO-NPs) have been synthesized by several methods such as sol–gel, chemical precipitation, chemical bath deposition, spray paralysis, hydrothermal, and laser ablation.…”